A woman walks through the pergola at Lake Merritt on Tuesday, May 14, 2014, in Oakland, Calif. Temperatures soared into the 90s across the Bay Area for the second consecutive day on and were expected to remain high through the end of the week. less

A woman walks through the pergola at Lake Merritt on Tuesday, May 14, 2014, in Oakland, Calif. Temperatures soared into the 90s across the Bay Area for the second consecutive day on and were expected to remain ... more

Tyler Gomez finds herself the target of children splashing water to keep cool at Lake Temescal in Oakland, Calif. on Tuesday, May 13, 2014. Rising temperatures are forecast to hit triple digits in some areas of the Bay Area on Wednesday. less

Tyler Gomez finds herself the target of children splashing water to keep cool at Lake Temescal in Oakland, Calif. on Tuesday, May 13, 2014. Rising temperatures are forecast to hit triple digits in some areas of ... more

Meghan Grady lays in the sunshine in Mission Dolores Park May 13, 2014 in San Francisco, Calif. Temperatures climbed to the mid 80s on Tuesday but they are forecast to drop back down by the end of the week.

Meghan Grady lays in the sunshine in Mission Dolores Park May 13, 2014 in San Francisco, Calif. Temperatures climbed to the mid 80s on Tuesday but they are forecast to drop back down by the end of the week.

Three boys played with a sprinkler head in the park area in front of the California Academy of Sciences Tuesday May 13, 2014 in San Francisco, Calif. Hot weather returned to the Bay Area and visitors to Golden Gate park did their best to stay cool. less

Three boys played with a sprinkler head in the park area in front of the California Academy of Sciences Tuesday May 13, 2014 in San Francisco, Calif. Hot weather returned to the Bay Area and visitors to Golden ... more

A couple sits in the shade along the shore at Lake Merritt on Tuesday, May 14, 2014, in Oakland, Calif. Temperatures soared into the 90s across the Bay Area for the second consecutive day on and were expected to remain high through the end of the week. less

A couple sits in the shade along the shore at Lake Merritt on Tuesday, May 14, 2014, in Oakland, Calif. Temperatures soared into the 90s across the Bay Area for the second consecutive day on and were expected ... more

Jace Brady, 2, waves to the ducks at Lake Merritt as he walked with his mom Nathalie Merchant, right, and his aunt Jen Merchant, left, on Tuesday, May 14, 2014, in Oakland, Calif. Temperatures soared into the 90s across the Bay Area for the second consecutive day on and were expected to remain high through the end of the week. less

Jace Brady, 2, waves to the ducks at Lake Merritt as he walked with his mom Nathalie Merchant, right, and his aunt Jen Merchant, left, on Tuesday, May 14, 2014, in Oakland, Calif. Temperatures soared into the ... more

SAN FRANCISCO, CA - MAY 13: A worker makes adjustments to sprinklers at Crissy Field on May 13, 2014 in San Francisco, California. The San Francisco Bay Area is experiencing record temperatures with San Francisco reaching 90 degrees on Tuesday, breaking the old record of 87 set in 1927. The heat wave throughout the Bay Area will taper off on Thursday. (Photo by Justin Sullivan/Getty Images) less

SAN FRANCISCO, CA - MAY 13: A worker makes adjustments to sprinklers at Crissy Field on May 13, 2014 in San Francisco, California. The San Francisco Bay Area is experiencing record temperatures with San ... more

A bicyclist on a path rides past a gondola at Lake Merritt on Tuesday, May 14, 2014, in Oakland, Calif. Temperatures soared into the 90s across the Bay Area for the second consecutive day on and were expected to remain high through the end of the week. less

A bicyclist on a path rides past a gondola at Lake Merritt on Tuesday, May 14, 2014, in Oakland, Calif. Temperatures soared into the 90s across the Bay Area for the second consecutive day on and were expected ... more

Beachgoers play in the surf at Ocean Beach on May 13, 2014 in San Francisco, California.

Beachgoers play in the surf at Ocean Beach on May 13, 2014 in San Francisco, California.

Photo: Justin Sullivan, Getty Images

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SAN FRANCISCO, CA - MAY 13: Beachgoers play fetch with dogs at Crissy Field on May 13, 2014 in San Francisco, California. The San Francisco Bay Area is experiencing record temperatures with San Francisco reaching 90 degrees on Tuesday, breaking the old record of 87 set in 1927. The heat wave throughout the Bay Area will taper off on Thursday. (Photo by Justin Sullivan/Getty Images) less

SAN FRANCISCO, CA - MAY 13: Beachgoers play fetch with dogs at Crissy Field on May 13, 2014 in San Francisco, California. The San Francisco Bay Area is experiencing record temperatures with San Francisco ... more

Photo: Justin Sullivan, Getty Images

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A man jogs up the Lyon Street stairs on May 13, 2014 in San Francisco, California. The San Francisco Bay Area is experiencing record temperatures with San Francisco reaching 90 degrees on Tuesday, breaking the old record of 87 set in 1927. The heat wave throughout the Bay Area will taper off on Thursday. less

A man jogs up the Lyon Street stairs on May 13, 2014 in San Francisco, California. The San Francisco Bay Area is experiencing record temperatures with San Francisco reaching 90 degrees on Tuesday, breaking the ... more

A young girl ran through a sprinkler to stay cool in the park area in front of the California Academy of Sciences Tuesday May 13, 2014 in San Francisco, Calif. Hot weather returned to the Bay Area and visitors to Golden Gate park did their best to stay cool. less

A young girl ran through a sprinkler to stay cool in the park area in front of the California Academy of Sciences Tuesday May 13, 2014 in San Francisco, Calif. Hot weather returned to the Bay Area and visitors ... more

A woman cooled her toes in a fountain in front of the California Academy of Sciences Tuesday May 13, 2014 in San Francisco, Calif. Hot weather returned to the Bay Area and visitors to Golden Gate park did their best to stay cool. less

A woman cooled her toes in a fountain in front of the California Academy of Sciences Tuesday May 13, 2014 in San Francisco, Calif. Hot weather returned to the Bay Area and visitors to Golden Gate park did their ... more

Dyson Kobayashi (second from left) and his friends keep cool at Lake Temescal in Oakland, Calif. on Tuesday, May 13, 2014. Rising temperatures are forecast to hit triple digits in some areas of the Bay Area on Wednesday. less

Dyson Kobayashi (second from left) and his friends keep cool at Lake Temescal in Oakland, Calif. on Tuesday, May 13, 2014. Rising temperatures are forecast to hit triple digits in some areas of the Bay Area on ... more

Rebecca Rich, 26, left, lays with Georgia O'Connor, 23, in the shade of a tree as they take a break to get out of the heat during their visit to the city from Sydney, Australia in Mission Dolores Park May 13, 2014 in San Francisco, Calif. Temperatures climbed to the mid 80s on Tuesday but they are forecast to drop back down by the end of the week. less

Rebecca Rich, 26, left, lays with Georgia O'Connor, 23, in the shade of a tree as they take a break to get out of the heat during their visit to the city from Sydney, Australia in Mission Dolores Park May 13, ... more

Eli Powelson and Ellen Cohan ride a paddle boat on Lake Merritt on Tuesday, May 14, 2014, in Oakland, Calif. Temperatures soared into the 90s across the Bay Area for the second consecutive day on and were expected to remain high through the end of the week. less

Eli Powelson and Ellen Cohan ride a paddle boat on Lake Merritt on Tuesday, May 14, 2014, in Oakland, Calif. Temperatures soared into the 90s across the Bay Area for the second consecutive day on and were ... more

Janay Freeman of Oakland cools sits by the edge of the water at Lake Merritt on Tuesday, May 14, 2014, in Oakland, Calif. Temperatures soared into the 90s across the Bay Area for the second consecutive day on and were expected to remain high through the end of the week. less

Janay Freeman of Oakland cools sits by the edge of the water at Lake Merritt on Tuesday, May 14, 2014, in Oakland, Calif. Temperatures soared into the 90s across the Bay Area for the second consecutive day on ... more

Jeff Johnson plays the saxophone at the pergola at Lake Merritt on Tuesday, May 14, 2014, in Oakland, Calif. Temperatures soared into the 90s across the Bay Area for the second consecutive day on and were expected to remain high through the end of the week. less

Jeff Johnson plays the saxophone at the pergola at Lake Merritt on Tuesday, May 14, 2014, in Oakland, Calif. Temperatures soared into the 90s across the Bay Area for the second consecutive day on and were ... more

Photo: Carlos Avila Gonzalez, The Chronicle

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Janay Freeman of Oakland sits by the edge of the water at Lake Merritt on Tuesday, May 14, 2014, in Oakland, Calif. Temperatures soared into the 90s across the Bay Area for the second consecutive day on and were expected to remain high through the end of the week. less

Janay Freeman of Oakland sits by the edge of the water at Lake Merritt on Tuesday, May 14, 2014, in Oakland, Calif. Temperatures soared into the 90s across the Bay Area for the second consecutive day on and ... more

Photo: Carlos Avila Gonzalez, The Chronicle

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Ronnell Stanton (left) and his buddy Arinn Brooks engage in a water fight at Lake Temescal in Oakland, Calif. on Tuesday, May 13, 2014. Rising temperatures are forecast to hit triple digits in some areas of the Bay Area on Wednesday. less

Ronnell Stanton (left) and his buddy Arinn Brooks engage in a water fight at Lake Temescal in Oakland, Calif. on Tuesday, May 13, 2014. Rising temperatures are forecast to hit triple digits in some areas of the ... more

Photo: Paul Chinn, The Chronicle

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Dyson Kobayashi sprays a stream of water towards friends at Lake Temescal in Oakland, Calif. on Tuesday, May 13, 2014. Rising temperatures are forecast to hit triple digits in some areas of the Bay Area on Wednesday. less

Dyson Kobayashi sprays a stream of water towards friends at Lake Temescal in Oakland, Calif. on Tuesday, May 13, 2014. Rising temperatures are forecast to hit triple digits in some areas of the Bay Area on ... more

Photo: Paul Chinn, The Chronicle

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Quinn Kobelak, 20, of Pittsburgh, Pennsylvania, found a shady spot, in a tree, to make a call outside the state Treasury Building while visiting Sacramento, Calif., Tuesday, May 13, 2014.

Quinn Kobelak, 20, of Pittsburgh, Pennsylvania, found a shady spot, in a tree, to make a call outside the state Treasury Building while visiting Sacramento, Calif., Tuesday, May 13, 2014.

Photo: Rich Pedroncelli, Associated Press

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Jace Brady, 2, waves to the ducks at Lake Merritt as he walked with his mom Nathalie Merchant and his aunt Jen Merchant on Tuesday, May 14, 2014, in Oakland, Calif. Temperatures soared into the 90s across the Bay Area for the second consecutive day on and were expected to remain high through the end of the week. less

Jace Brady, 2, waves to the ducks at Lake Merritt as he walked with his mom Nathalie Merchant and his aunt Jen Merchant on Tuesday, May 14, 2014, in Oakland, Calif. Temperatures soared into the 90s across the ... more

Swimmers take advantage of a free senior swimming day at Lions Pool in Oakland, Calif. on Wednesday, May 14, 2014. Mayor Quan and Parks & Recreation Director Audree Jones-Taylor worked to open up free swimming for seniors at Oakland city-owned pools and for everyone at East Oakland Sports Center. less

Swimmers take advantage of a free senior swimming day at Lions Pool in Oakland, Calif. on Wednesday, May 14, 2014. Mayor Quan and Parks & Recreation Director Audree Jones-Taylor worked to open up free ... more

Photo: Tim Hussin, Special To The Chronicle

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Swimmers take advantage of a free senior swimming day at Lions Pool in Oakland, Calif. on Wednesday, May 14, 2014. Mayor Quan and Parks & Recreation Director Audree Jones-Taylor worked to open up free swimming for seniors at Oakland city-owned pools and for everyone at East Oakland Sports Center. less

Swimmers take advantage of a free senior swimming day at Lions Pool in Oakland, Calif. on Wednesday, May 14, 2014. Mayor Quan and Parks & Recreation Director Audree Jones-Taylor worked to open up free ... more

Photo: Tim Hussin, Special To The Chronicle

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Heat records shattered across Bay Area

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Temperatures across the region soared to historic levels Wednesday, marking the hottest day of the year in most areas.

Oakland hit a whopping 93 degrees, breaking its old record of 89 for the date. San Jose tied its record of 94, while Santa Cruz reached a historic 100 degrees.

San Francisco, too, hit a record high of 88 for the date, but unlike most areas, the city was slightly cooler Wednesday than it was Tuesday, when the mercury hit 90.

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The weather service had a heat advisory in effect through Wednesday evening, warning residents to take common-sense measures to stay cool, such as drinking plenty of water.

The region's highest temperatures Wednesday were recorded in the South Bay, where Gilroy and Morgan Hill both hit 102 degrees.

A high-pressure system is responsible for the heat wave. A trough of low pressure from the Pacific Ocean is expected to begin moving toward the West Coast on Thursday, breaking down the high-pressure ridge.

Wednesday "should be the zenith, and (Thursday) we're looking at a reduction in temperatures of upwards of nearly 10 degrees in some places," said Diana Henderson, a weather service meteorologist.